Children with signs of MCT8 deficiency, such as failure to thrive, tachycardia, hypotonia, and delayed developmental milestones, may then be referred to a developmental pediatrician, pediatric neurologist, cardiologist, endocrinologist, gastroenterologist, or nutrition specialist, depending on the individual patient's specific symptoms and severity of presentation (1, 4). The gene discussed is SLC16A2; the disease is hyperinsulinemic hypoglycemia, familial, 4.